A number of folding knife configurations have been used in the past. FIG. 1 depicts a knife generally of the type described in U.S. Pat. No. 3,942,249 issued Mar. 9, 1976 to Mr. Paul W. Poehlmann. In this device, a handle is formed by left and right side plates, 1007, 1008 sandwiching a spacer 1009 and held together by rivets 1011 and 1012. A blade 1041 is coupled to the handle so as to be rotatable about axis 1018 from the extended configuration depicted in FIG. 1 to a folded configuration with the blade 1041 adjacent the spacer 1009 and substantially between the sideplates 1007 and 1008. A key locking mechanism made up of hub 1021, spring 1056, detent 1048 and nut 1036 resides in openings 1016, 1043, 1029 in the left plate 1007, blade 1041 and right plate 1008 respectively. Keys 1052, 1053 interact with keyways 1044, 1046, 1038, 1039 in the blade 1041 and right plate 1008 respectively. In the normal configuration, the key locking mechanism is configured so that the keys 1052, 1053 reside partially in the blade keyways 1044, 1046 partially in the plate keyways, 1038, 1039. Thus locking the blades 1041 in a position with respect to the handle. When the user pushes on the activation surface of the key locking mechanism, (e.g. depressing right surface of the detent 1048) the keys 1052, 1053 are moved, against the urging of spring 1056 so as to reside solely within the blade keyways 1044, 1046 and to be clear of the plate keyways 1038 and 1039. With the activation surface so depressed, the key locking mechanism can be rotated, carrying the blade 1041 with it and rotating the blade 1041, e.g., from the extended configuration to the folded configuration or vice-versa. After such rotation, once the detents 1053, 1052 are aligned with the plate keyways 1038, 1039 the spring 1056 will urge the key device back into the relaxed configuration such that the keys 1053 1052 reside partially in the blade keyways 1044 1046 and partially in the plate keyways 1038, 1039 thus locking the blade in the folded configuration.
Although the configuration shown in FIG. 1 has proved to be useful and desirable for a multitude of purposes, it can be difficult and/or expensive to produce the device with sufficient accuracy e.g. to achieve a desired degree of locking of the blade with no play. In most cases, using normal manufacturing tolerances, a knife which is configured with tolerances to permit the detents 1052, 1053 to slide easily in the keyways 1044, 1046, 1038, 1039 may often result in a locked configuration which has an undesirable amount of play, i.e., in which the blade 1041 can rotate a small amount with respect to the handle, even in the locked position. Furthermore, the configuration depicted in FIG. 1 is such that the blade in the extended position is exactly 180.degree. rotationally displaced from the blade in the closed or folded configuration, which places undesirable constraints on the knife design and restricts the perimeter design of the blade. In knives which provide for the meeting of stop surfaces, some geometries caused undesirable movement of forces on components, upon such meeting, because of a resultant camming action of the respective parts. Furthermore, in the embodiment of FIG. 1, there may be an undesirable amount of blade play in the extended position.
Accordingly, it would be useful to provide a folding knife which provides for secure locking in the extended and folded configuration with minimum play, which permits locking after a rotational blade displacement of other than 180.degree., preferably less than 180.degree. and/or which has improved ease or economy of design, manufacture, repair and/or maintenance.